One category of copolymers having good flexibility is the siloxane polyether (SPE) copolymers. These SPE copolymers are generally considered as nonionic “surface active” agents and one of their uses is for the preparation of various types of emulsions. There are many commercially available SPE copolymers. These block copolymers are of two types. One SPE copolymer type is prepared by the platinum complex catalyzed hydrosilation reaction of hydride functionalized polydimethylsiloxanes with alkenes. The hydrosilation prepared SPE copolymers contain Si—C—C linkages and can be named alkyl-SPE. There are several commercially available alkyl-SPE copolymers, such as Dow Corning 2-8692 fluid or the Silwet series from GE Silicones. There are many diverse uses for these copolymers, such as nonionic surfactants and defoamers. However the preparation method used for alkyl-SPE, namely hydrosilation, suffers from the disadvantage that it never goes to completion, always resulting in the starting materials being present in the final product, especially the alkene reactant in non-negligible amounts, e.g., at 10% or higher, and other unsaturated impurities such as enol ethers. These impurities are difficult to remove by distillation due to high boiling point. The presence of allyl ethers in the SPE does not generally interfere with many commercial uses of these products, such as for surfactants. However when these SPE copolymers are further functionalized with vinyl groups and included in 2 part addition silicone impression material formulations, these impurities cause slowing of the hydrosilation reaction. Use of such copolymers requires a higher concentration of platinum catalyst to get sufficient physical properties and it is likely they cannot be included in the catalyst side due to compromised shelf life. Despite these limitations, several polymerizable SPE are described in the patent literature for use in addition silicone impression materials used in dentistry, apparently all of them obtained via a hydrosilation reaction. These are Stepp U.S. Pat. No. 5,580,921 (Wacker), Kamokora U.S. Pat. No. 6,861,457 (GC Corp) and Bublewitz US2008319100A1 (Kettenbach) and other related publications. There is therefore a need for a preparation method for an SPE without unsaturated impurities being present in the final product.
Another SPE copolymer type is prepared by a condensation reaction, that is, by the coupling of a chlorine or acetoxy substituted polydimethylsiloxane (PDMS) with an alcohol to afford alkoxy substituted PDMS, but this method suffers from the difficulty of removing the hydrochloric acid or other acid waste and is relatively expensive to scale to large amounts. The condensation prepared SPE copolymers contain Si—O—C linkages and can be named alkoxy-SPE. The alkyl-SPE copolymers are more hydrolytically stable than the alkoxy-SPE in strongly acid conditions. However in neutral or weakly acid or basic conditions (such as physiologic pH) their hydrolysis rates are comparable.
The dehydrogenative sylilation of hydride functionalized siloxanes and alcohols is a known synthetic route to highly pure alkoxy functionalized siloxanes (see, e.g., PMSE 2005, 92, 365; PMSE 2004, 91, 587). This dehydrogenation is carried out in the presence of a very strong Lewis acid catalyst, such as tris(pentafluoro-triphenyl)borane, B(C6F5)3. This preparatory route is convenient since the byproduct, hydrogen gas, is easy to remove as opposed to the chlorosiloxane route that gives difficult to dispose of hydrochloric acid.
The dehydrogenation of hydride-functionalized polyorganosiloxanes with alcohols has been described in U.S. Patent Application Publication No. US 2004/0186260 ('6260 publication) submitted by Goldschmidt AG. The process disclosed therein is for preparing alkoxy-substituted polyorganosiloxanes using the dehydrogenation reaction in the presence of a main group III and/or transition group III catalyst and optionally a solvent. Specifically, the '6260 publication contains examples relating to the reaction of hydride terminated (alpha, omega disubstituted and/or tethered (comb-like)) polyorganosiloxanes with simple alcohols and simple alcohol started polyethers. However, the '6260 publication does not disclose any specific copolymers or method of making same that provide the desired results in an addition silicone based dental impression material.
In dentistry, addition silicones are the most widely used impression materials. Addition silicones cure with a hydrosilation mechanism and contain a platinum compound as a catalyst. Despite the addition of various surfactants, the hydrophilicity of the materials as measured by contact angle measurements, especially before set is completed, is very low. This reduces the ability of the impression material to displace oral fluids during curing and results in a compromised impression. Moreover, increased use of non-ionic surfactants leads to extraction into oral fluids producing an undesirable taste. Since these non-ionic surfactants are non-polymerizable, increased amounts used can also lead to weakening of the elastomer upon curing. Another class of impression material, the polyethers, as exemplified by IMPREGUM® (from 3M ESPE) are 2-part systems containing imine terminated polyether copolymers cured by reaction with a strong acid. However, these polyethers suffer from high rigidity, which is a property of crosslinked polyethers, and poor taste and smell due to the presence of imines and strong acids.
There is thus a need for a vinyl functionalized alkoxy-SPE copolymer with properties that can be used as a resin component together with a vinyl functionalized siloxane, both curable via a hydrosilation reaction for use in a dental impression material, and a process of making the same.